Vapor generating and superheating unit with vapor temperature controls



March 10, 1959 H. H. NELKEN 2,376,748

VAPOR GENERATING AND SUPERHEATING UNIT WITH VAPOR TEMPERATURE CONTROLSFiled Feb. 9, 1954 5 Sheets-Sheet l SUPERHEATER FURNACE I I I I I I I II I l I I I x I I I I I I l -I I I l I 170 .506 /72' I66 I 64 lNV TORMarch 1959 H H.- NELKEN 2,876, 48

VAPOR GENERATING AND SUPERHEATING'UNIT WITH 1 VAPOR TEMPERATURE CONTROLST Filed Feb. 9, 1954 5 Sheets-Sheet 2 TMIIJA.

PRIM.S.H. STAGE 2 ATTORNEY March 1959 H. H. NELKEN 2,876,748

VAPOR GENERATING AND SUPERHEATING UNIT WITH VAPOR TEMPERATURE CONTROLSFiled Feb. 9, 1954 5 Sheets-Sheet 3 H.Nelken I ATTORNEY March 10, 1959H. H. NELKEN 7 VAPOR GENERATING AND SUPERHEATING UNIT WITH VAPORTEMPERATURE CONTROLS Filed Feb. 9, 1954 5 Sheets-Sheet 4 TlEfE- I l PRIMSH 1 mi; A- i //2 i l i I X I /74f PRIM SH. STAGE 1 Numb ' ATTORNEYMarch 10, 1959 H. NELKEN I 2,376,748

VAPOR GENERATING AND SUPERHEATING UNIT WITH VAPOR TEMPERATURE CONTROLS 1Filed Feb. 9, 1954 5 Sheets-Sheet 5 PRIMARY REHEATER SUPE RHEATER T33 Ielken ,tion in the cost of generated power.

VAPOR GENERATING AND SUPERHEATING UNIT WITH VAPOR TEMPERATURE CONTROLSHarvey H. Nelken, River Edge, N. J., assiguor to The Bab'cock & WilcoxCompany, New York, N. Y., a corporation of New Jersey ApplicationFebruary 9, 1954, Serial No. 409,086

13 (Ilaims. (Cl. 122-240) This invention relates to a vapor generatingand superheating-unit. I t

The invention is more particularly concerned with a vapor generating andsuperheating unit of the radiant boiler type and having its componentsso constructed and arranged that it provides for the reliable operationof the unit with a high degree of availability. The vapor generating andsuperheating unit of the invention is capable of producing 1,700,000pounds steam per hour at a temperature of the order of 1100 F. and at apressure in excess of 2000 p. s. i. with minimum requirements as tospace occupied by the unit and when combined with the other necessarycomponents for the production of electric power. In addition, the unitis capable of producing power at a greatly reduced cost of vapor perunit of power.

More specifically, the invention involves a vapor generating andsuperheating unit of the radiant boiler type having a large volumefurnace, with its rectangular cross section of the order of 60 x 30feet, and with its height of the order of 150 feet. The furnace has aplurality of lateral outlets at its upper part leading in parallel fromthe longer side of furnace cross section. These outlets lead to paralleland separate gas pass constructions each having its own set of liquidcooled enclosing walls, and with the gas passes spaced from each otherso as to facilitate accessibility and promote effectiveness ofstructural support. A convection vapor superheater or reheater isarranged in each gas pass and when, for example, the superheater has aconvection section in each of the separate gas passes, these twosections are crossconnected in series as to vapor flow in order that thevapor temperature at the final outlet of the vapor heater is notaffected by unbalanced gas flow in the two parallel gas passes.

The illustrative unit being of the capacity of the order of 1,700,000pounds of vapor per hour, marks a milestone in the progress of the artof steam generation and steam superheating in units assoicated withsteam turblues and electric generators for electrical power production.One of the outstanding accomplishments in this art is represented by thepresent invention which attains, with its associated power plant units,a marked reduc- To a considerable extent, this result is attained by themagnitude of the steam generating and superheating unit, but, inaddition, the fabrication of such a large unit is something more than amere enlargement of previously suggested units. For example, althoughthere have been suggested in the prior art, units of the type of theillustrative unit, the suggested units having radiant boiler furnaces ofthe order of 30 feet square in horizontal cross section with a height offrom 60 to 90 feet. When a unit was considered of a capacity almostdouble that of the suggested units, serious problemswere encountered.One such problemrelated to the limitation on the minor dimension of thecross section of such a gas pass, such limitation being imposed by thecharacteristics of the .retractible to the superheater.

2,876,748 Patented Mar. 10, 199

ice

soot blowing apparatus necessary for periodic use in the cleaning of theconvection surfaces in the associated gas passes. Such cleaning devices,even when employed from opposite sides of a furnace or a gas pass,impose a restriction of the minor cross section dimension of that gaspass of the order of 20-25 feet. Also, because the soot blowers areretractible there is a minimum withdrawal space necessary externally ofthe unit, to keep the cost of the unit within a reasonable range. Theillustrative unit meets these requirements while at the same timeproviding a unit of a capacity far beyond the for the superheaters,reheaters and other convection heating apparatus, and by arranging theparallel gas passes as" entirely separate enclosures with their adjacentwalls spaced from each other sufliciently to provide for manual accesstherebetween for the purposes of maintenance, cleaning and repair. Theillustrative unit also promotes the maximum capacity within a givenspace requirement by providing that the parallel passes lead from thesame face or side of the furnace, or its rectangular cross sectionoutlet.

For optimum vapor or steam heating, the invention not only providescross connected secondary superheater sections which 'are disposed inseparate gas passes leading in parallel from the combustion zone, theinvention also provides for superheat and reheat control. To this endthe reheater surface is disposed in one of the parallel gas passes andat least the major part of the primary superheater surface is disposedin the other gas pass.

The total secondary superheater surface is divided be-- tween the twogas passes.

In connection with the vapor heating provisions referred to immediatelyabove there is a recirculated gas system affecting each gas pass, takingpartially cooled parts of the load range,'so as to overcome, forinstance;

the natural tendencies of convection vapor heaters to fail to develop apredetermined high temperature 'over such lower portions of the loadrange.

The invention also involves attemperation as a part of the entirecontrol setup, but this attemperation is limited Preferablyattemperation takes place in the steam flow at a position between theprimary superheater and the secondary superheater.

In addition to the 'above mentioned components invention involves theproportioning' of the total gas flow; between the two gas passes for thepurpose of controlling vapor temperature, and particularly reheattemperature. The various features of novelty which characterize myinvention are pointed out with particularity in the claims annexed toand forming a part of this specifica tion. For a better understanding ofthe invention, its operating advantages and specific objects attained byits use, reference should be had to the accompanying drawings anddescriptive matter in which I have illustrated.

ating and superheating unit, on the line 1-1 of Fig. 2;-

Fig. l-A is another vertical section of the same unit,

p on the line 1A-1A of Fig. 2;

Fi 2 s a Pl n ecti n t he ame n on h line 2-2 of Fig. 1;

Fig. 3 is an isometric diagrammatic view of the convection components ofthe Fig. 2 unit; and

Fig. 4 is a vertical section of another unit embodying some of thefeatures of the Fig. 2 unit.

The vapor generating and superheating unit shown in Figs. 1-3 has acombustion component including two vertically elongated furnaces 10 and12 defined by upright vapor generating wall tubes including the tubes ofthe division wall 14, separating the furnaces. The furnace 10, furthershown in Fig. 1, is fired by vertically spaced rows of burners 16, 18and 20 and the other furnace 1 2, shown in Fig. 1A is similarly fired byrows of burners 22, 24 and 26.

The vapor generating tubes of the furnaces discharge generated vaporinto the drum at a rate of the order of 1 9 Po s o ap P r ou at a pres ohe rder of; 23 0 p unds. per squar nch he n ra apor item he r s uperh edto a p t re ot the order of 10 50 F. in convection superheater sectionsselectively disposed in two convection gas passes leading from thefurnace. One gas pass leads directly rearwardly from the furnace 12 andthe other, parallel to the first, leads directly rearwardly from theother furnace 10, as shown in Figs. 1 and 2. Fig. 1A shows the gas passleading from the furnace 12.

The Fig. 1 gas pass 32 includes a lateral sub-pass 34 at the upper partof the unit discharging gases into the gas turning space 36 from whichthe gases proceed through the downpass 38. In the lateral sub-pass 34the high temperature gases first pass over the pendent superheatersection 40, constituting stage 2 of the secondary superheater, fromwhich vapor superheated to a temperature of the order of 1050 F. passesto a high pressure prime mover such as a turbine. From the second stage40 of the secondary superheater the gases next pass over the bank ofhorizontally spaced upright tubes 42 constituting stage 1 of a primarysuperheater.

Beyond the primary superheater stage 1 the gases turn in the space 36and pass downwardly over the successive banks 44-46 of horizontal tubesconstituting the leading part of stage 1 of the primary superheater.These banks of tubes, as well as the bank of upright tubes 42 are formedby continuous, or serially connected tubes receiving vapor at theirinlet ends from header components 48-50. connected, in turn, to thedischarge ends ofsuperheater supply wall tubes, disposed along the wallsof the downpass 38. The inlet ends of these rows of wall tubes 52 and 54are in communication with the vapor space of the drum 30. A similararrangement of superheater supply wall tubes is associated with theother downpass 106. In this downpass 106 vapor passes from superheatersupply wall tubes to the headers 1-16', 118 and 120 and thence throughappropriate conduits to the inlet header components 48, 4-? and d at thebottom of downpass 38. The header components 116, 118 and 120 aredisposed at the walls of downpass 106. The superheater supply wall tubes122 and 124, for headers 116, 118 and 120 are arranged along the gaspass walls and having their inlet ends in communi cation with the vaporspace of the drum 3%), through connections such as the header 123 andthe conduits 125.

Below the banks of tubes 44-46 of stage 1 of the primary superheater theheating gases next pass over the tubes of the economizer 56 and thenthrough the ductwork 58 to the regenerative air heater 60. The ductwork58 has mounted therein a row of gas flow regulators 62 for proportioningthe flow of heating gases over the pertinent vapor heaters (i. e.,primary and secondary superheater components) Below the air heater 60ductwork 64 is provided for flow ofthe gases to a flueor stack.Secondary air passes to the other side of the air heater from a forceddraft fan 66 and interposed ductwork 68; From the air outlet side of theair heater, heated air flows through ductwork 70, 72, to the windbox 74enclosing the bumers 16, 18 and 20.

Fig. 1A shows the gas pass leading from the fur nace 12, this gas passstructure being separated from the gas pass 32by access and maintenancespace 82, as indicated in Fig. 2. This space advantageously enhancesmaintenance of the illustrative unit by facilitating the installationand use of elfective soot blowers from positions between the gas passes32 and 80.

The gas pass 80 includes the lateral, or horizontal, sub-pass 84. Gasesentering this sub-pass first contact the horizontally spaced uprighttubes of the bank of tubes 86 constituting stage 1 of the secondarysuperheater. These tubes lead from the inlet header 88 to the outletheader 90.

Upon leaving stage 1 of the secondary superheater (bank of tubes 86) thegases next pass over and between the horizontally spaced upright tubesconstituting the bank of tubes 92 of the second reheater stage, thesetubes leading from the inlet header 94 to the twin outlet headers 96 and98.

After leaving reheater stage 2 the gases pass over and between thespaced upright tubes constituting the bank of tubes 100 of reheaterstage 1, these serially connected return bend tubes being pendentlysupported, at least in part, from the inlet header 102 and outlet header104.

The reheater stage 1 (bank of tubes 100) is disposed in a gas turningspace above a downpass 106 in which the banks of tubes 108110 of stage 2of the primary superheater are disposed. These serially connected returnbend tubes lead from the lower inlet header 112 to the outlet header114, disposed above the gas turning space in which stage 1 of thereheater is located.

The inlet header 112 receives vapor through connections 174 and 176 fromprimary superheater first stage outlet header 43.

At the lower end of the downpass 106 there is a series of gas flowregulators 126 for controlling gas flow over stage 1 of the secondarysuperheater (bank of tubes 86), reheater stage 1, reheater stage 2, andstage 2 of the primary superheater, all disposed in the gas pass 80.

It is within the purview of the invention that the gas flow regulators126 together with their counterparts 62 in the other gas pass and acommon control system, acting from reheat temperature and load, shallfunction as gas flow proportioning means to maintain a predeterminedreheat temperature over a wide load range and this action shall obtainwhether the gas flows are subject to a common recirculated gasconnection, or not. Such a common connection may involve a unitary ductformed by the ducts 156 and 166.

Where such a unitary duct is involved, the windboxes 74 and 136 may alsoconstitute an integral windbox and the gas passes 38 and 106 may beconnected by a common duct below the economizers therein.

Beyond the gas flow regulators 126 the gases flow through a duct 128 tothe regenerative air heater 130 from which heated secondary air flowsthrough ductwork components 132 and 134 to the windbox 136 disposedaround the rows of burners 22, 24 and 26. Air flows through duct 138from the forced draft fan 140 to the air heater, and the heating gasesflow from the air heater through ductwork 142 to a stack.

Fig. 2 shows a horizontal section of the furnace division wall 14,constructed of wall aligned vapor generating tubes having their upperparts oppositely bent out of their wall alignment to form the platens14a and 14b spaced as shown to provide inter-communication be tween thefurnaces for pressure equalization and for gaseous movements in responseto the. control of gas proportioning between the gas passes, 32. and 80or in response to other furnace. gas flow control such as the variationin flow of recirculated gases to the. furnaces. to control reheat. TheFig. 1A gas pass (also indicated asp-awasin Fig. 2 as the gas pass 80)may be termed a reheater gas pass, since all of the reheater surface isdisposed therein. Likewise, the furnace 12 of Fig. 1A might be termedthe reheater furnace. It is provided with a hopper bottom 144 into andthrough the throat 146 of which are discharged partially cooled heatinggases from an opening or passage 158 leading from the manifold 156. Thesystem for effecting such recirculation includes a duct 150 connectingan opening 148 in duct 128 with the inlet of a recirculated gas fan 152.The outlet of the fan is connected by a duct 154 to the manifold 156from which a plurality of outlet ducts 158 are in communication with thethroat 146.

When operating conditions are changed in such a way as to have atendency to cause reheat vapor temperature to drop below its optimumvalue of 1000 F. as when the load decreases, the flow of recirculatedgas through the above described system and thence through the furnace 12and its gas pass is increased to increase gas mass flow over thereheater stages and thereby have a corrective influence at leastpartially offsetting the tendency of reheat temperature to drop. Thiscorrective influence may be combined with automatic control of the gasproportioning dampers, 126 and 62, to attain a predetermined reheat, orthe latter control may be used alone to attain the same eifect.

A similar recirculated gas system is shown in Fig. 1 as applied to thesuperheater furnace 10. It includes a duct 160 connecting a recirculatedgas inlet 162 in ductwork 58 with the inlet of a fan 164 the outlet ofwhich is connected to the recirculated gas manifold 166 by a duct 168.The manifold is connected with the hopper bottom throat 170 by aplurality of outlet ducts 172 distributed throughout the length of themanifold.

The illustrative unit further promotes control of vapor temperature onthe reheater and superheater sides by proportioning gas Weight or gasflows through the separate gas passes and their furnaces by means of thepro portioning dampers or gas flow regulators 126 (Fig. 1A) and 62 (Fig.1). Preferably such proportioning of gas flows through the separate gaspasses 32 and 80 is utilized, in the illustrative unit, to adjust reheattemperature in reference to superheat, or primarily for maintaining apredetermined reheat temperature, and control of recirculated gas flowis effected to maintain superheat temperature at a predetermined value.control and recirculated gas flow control are efiected Bothproportioning automatically from combinations of influences in both ofwhich load is a factor. In the propo-rtioning combination reheattemperature is also involved as an influence, and in the recirculatedgas flow control combination superheat temperature is involved.

The pertinent system and arrangement of superheater-s and reheaters andtheir connections (shown in perspective or isometric form in Fig. 3)avoids any substantial unbalance of secondary superheater heatingeffects which might otherwise occur as a result of the arrangement ofsuperheater and reheater furnaces and their separate furnaces and gaspasses. As here shown, steam (from the drum enters the header at thelower end of the downpass 38 which receives gases from the superheaterfurnace 10. The header 50 receives the steam from header components 48,49, 116, 118 and 120 which, in turn, are directly connected to the vaporspace of the drum by superheater supply wall tubes, such as 52, 54, 122and 124, header 123 and tubes 125. The headers 116, 118 and 120 aredirectly connected to the header 50 by appropriate pipes or conduits(not shown). From this header 50 steam flows through the banks of tubes44, 45, 46 and 42 of stage 1 of the primary superheater to the outletheader 43 and thence through the parallel lines 174 and 176 to the inletheader 112 of stage 2 of the primary superheater in the gas pass leadingfrom the reheater furnace 12. From this header the steam (or vapor)flows through the tubes of the banks of tubes 10,8, 109 and to theoutlet header 114.

Lines 178 and 180 lead through appropriate attemperators (not shown) andconduct the superheated steam from the primary superheater outlet header114 to the inlet header 88 (secondary superheater stage 1) and thencethe steam flows through the bank of tubes 86 of stage 1 of the secondarysuperheater to the outlet lines and 192 conduct exhaust steam from aturbine stage to the inlet header 102 of stage 1 of the reheater. Itthenpasses through the bank of tubes 100 to the outlet header 104. Thence itis conducted to the inlet header 94 by the plural lines 194 and 196.From header 94 steam passes through the tubes 92 to the twin outletheaders 96 and 98. Thence the reheated steam returns to the turbine forfurther use.

The Fig. 4 vapor generating and superheating unit has verticallyelongated furnaces 200 and 202 defined by vapor generating tubes andfired by burners 204209 in a manner similar to that of the previouslydescribed unit. However, the convection gas pass from the reheaterfurnace 202 leads laterally to the right from the upper part of thatfurnace, over the second stage 210 of the secondary superheater and theninto a gas turning space 212. Thence the gases proceed downwardlythroughthe downpass 214 and over the banks of tubes 216, 217, 218, 220 of areheater having an inlet header 222 and twin outlet headers 224 and 226from which reheater outlet lines 228 and 230 lead to a turbine.

The entrance for the gas pass leading from the superheater furnace 200is directly opposite the entrance of the gas pass leading from thefurnace 202, the gases passing to the left from the upper part of thefurnace 200 through a horizontal gas pass component and over the banksof tubes 232 and 234 of the first stage of the secondary superheater.Thence the gases pass into the gas turning chamber 236 and thendownwardly through the primary superheater gas pass.238 in which arelocated the banks of horizontally disposed return bend tubes 240-244constituting the primary superheater through which steam passes from theinlet header 25 to the outlet header 252.

Superheated steam from the primary superheater outlet header 252 flowsupwardly through the conduits 254 and then through superheatattemperators 256 to the inlet header 258 for stage 1 of the secondarysuperheaten,

272 and 274 leading to the inlet header 276 of stage 2- of the secondarysuperheater. From this stage the superheated steam passes through thetwin headers 278 and 280 and through the connected superheater outlets282 and 284 to a point of use.

Saturated steam from the steam and water drum 300 passes throughsuperheater supply tubes 302 and 304 leading in opposite directions fromthe drum and along the roof of the unit. Some of the conduits 302 lead.

to the superheater inlet header 306 from which'wall tube connections 308lead to the rear superheater supply wall tubes 310 and along the rearwall 312 to the header 314 at the bottom of the reheater gas pass.

Others of the conduits 302 conduct saturated steam from the drum 300 tosuperheater supply side wall headers 316 from which superheater supplywall tubes 318 lead downwardly to connection with the superheater supplyheader component 318' at the bottom of the reheater pass. The headercomponents 318' and 314 are connected with a cross conduit 321 leadingto similarly disposed header components 250 and 320 at the left handside of the unit and at the bottom of the primary superheater gas pass.

At the opposite side of the unit the superheater supply conduits 304lead to the header 322 from which the tubes 324 lead to superheatersupply wall tubes 326 along the left hand wall 328 of the primarysuperheater gas pass. They lead downwardly along that wall to connectionwith the header 250. Other tubes 330 lead downwardly from the header 322and then through roof portions 332 and then through wall tubes alsodisposed along the wall 328. Others of the superheater supply conduits304 conduct saturated steam along the roof of the unit and thendownwardly to side wall headers 334 from which side wall tubes 336 leadto both of the side wall header components 320. Thus some of thesaturated steam passes from the drum 300, is superheated in the walls ofthe reheater gas pass and then passes to the primary superheater inletheaders 250 and 320 from which it flows through the primary superheaterincluding the banks of tubes 240244.

At the lower part of the primary superheater gas pass there is aneconomizer section 340. After passing over the tubes of this economizersection the gases pass downwardly, subject to the proportioning flowregulation of the dampers 342. Then they pass into breeching 344 whichis provided with a lateral outlet 346 from which part of the gases passthrough ductwork 348 to the inlet of a recirculating fan 350, the outletof which is connected by the ductwork 352 to a manifold 354 from whichspaced gas outlets 356 distributed along the length of the manifold leadinto the throat 358 of the hopper bottom of the superheater furnace 200.The flow of recirculating gases through the system including therecirculated gas fan 350 is controlled in such a manner as to increase(toward an optimum) superheated and reheat steam temperatures bycontrolling the speed of the fan 350 and/or regulating appropriatedampers associated with the ductwork 348. Such control may be efiectivcfrom appropriate variable influences such as representations of load,and superheat temperature.

At the opposite side of the unit, and at the lower end of the reheatergas pass including the banks of reheater tubes 216, 217, 218, 220, thereare banks of tubes 360 and 362 of another economizer section. Gases passfrom these economizer sections through and between the proportioningdampers 364 to breeching 366 in, one wall of which there is arecirculated gas outlet 368 connected by ductwork 370 to the inlet of arecirculated gas fan 372. The outlet of this fan is connected byductwork 374 to a manifold 376 from which regularly spaced recirculatedgas outlets 378 distributed along the length of the manifold lead intothe throat 380 of the hopper bottom of the reheater furnace 202. Thisrecireulated gas system may be controlled in the manner indlcated in thedescription of the recirculated gas system at the opposite side of theunit.

The Fig. 4 unit is subject to gas proportioning between the two furnacesections and the pertinent gas passes leading therefrom, for adjustmentof reheat, with respect to superheat, over a wide load range. Suchproportioning may be effected by the dampers 364 at the outlet end ofthe reheater gas pass and/or by the appropriate control of the dampers342 at the outlet end of the primary superheater gas pass.

The wall tubes of the furnaces 200 and 202 are connected into thecirculation of the unit by means of apptopriate large, diameterdowncomers 400 leading down-.

watdly from the water space of the. drum 30.0,, and through theintermediacy of appropriate headers and conduits including the hopperbottom headers 402-407 which are connected to furnace wall tubes.

The furnace sections 200 and 202 are separated by a division wall 420formed by closely spaced steam generating tubes leading upwardly fromthe hopper bottom headers 402 and 403. At the lower parts of thefurnaces these division wall tubes may be tangent so as to constitute afairly gas-tight wall, but at the upper part of the furnace sectionsadjacent division wall tube sections,

such as 422 and 424, are separated so as to form pressure equalizationpassages between the sections of the furnace. In both of theillustrative units there are two gas passes leading in parallel fromseparately fired furnaces.

In both units one of the gas passes has disposed therein all of thereheater surface while the other gas pass has a predominant proportionof the total primary superheater surface. Also, in both units, the totalsecondary superheater surface is divided between the two gas passes withthe steam or vapor flowing through one of the secondary superheaterstages and then through the other. Each unit discloses a recirculatedgas system for each gas pass and its associated furnace, and each unit,similarly, includes attemperators for superheat control.

In the operation of the illustrative units the flow of recirculated gasis increased when there would otherwise be a drop in temperature of thevapor at the secondary superheat outlet. This permits a predeterminedsuperheat to be attained over a wide load range, and particularly at lowloads.

Generally, the flow of recirculated gas is so controlled as to effect adesired vapor temperature of superheated vapor, and this is particularlytrue at the lower part of the load range. Such control, of course, inthis part of the load range, means that the flow of recirculated gasover both the superheater and the reheater stages will be increased.

Proportioning of gas flow between the two gas passes leading from theseparate furnace sections is also used for steam temperature control.Here, again, this proportioning is controlled primarily to maintainreheat at the desired value and if this action has a tendency to resultin the increase of superheat above the predetermined value, then theattemperators are operative to maintain the superheat at the desiredvalue. The gas flow proportioning between the two gas passes ispreferably effected by automatic control of one or both sets of thedampers, such as 342 and 364 in the Fig. 4 modification, and 126 and 62in the other modification.

The above described control system can be further augmented bydifferential firing of the furnaces.

It is within the purview of the invention that the control of the, gasflow regulators for gas proportioning, the control of the attemperators,and the control of the separate recirculated gas flow systems, would beautomatically controlled from a set of appropriate variables, such asthose mentioned above.

Referring again to Fig. 1 of the drawings, it is to be noted that throatis a passage formed by tube supported walls 500 and 502, the lower partsof which are inclined so as to direct the incoming recirculated gasessomewhat in the direction indicated by the arrow 504. The gases thusproceed toward the right hand furnace wall 506 and when the burners,such as 16, 18 and 20, are short flame turbulent burners, thecontinuance of the recirculated gases as a stratum along the wall 506 ispromoted.

Under some velocity conditions of the gases entering the lower part ofthe furnace 10, the recirculated gases, or a part of them, may also actto fill up the lower part of the furnace, with the higher density andlower temperature gases, thus rendering the lower part of the furnacerelatively inefiective as to the absorption of radiantly transmittedheat for vapor generation in the wall tubes of that part of thefurnace... The interposition of a thick stratum of recirculated gasesimmediately adjacent the gamma.

wall 506 also results in the reduction of heat absorption by the steamor vapor generating tubes along that part of the wall covered by thestratum. Such reduction in the furnace heat absorption preferably takesplace with an increase of the amount ofrecirculated gases entering thefurnace, and it correspondingly decreases the rate of vapor generation.

concomitantly, with the reduction of furnace heat absorption atdecreasing load, the increase in the amount of recirculated gasesaffords an increase in the gas mass flow over the convection banks ofvapor heating tubes disposed in the gas pass beyond the furnace and thuscompensates for an inherent tendency of such convection heaters toresult in undesirably low temperatures at the outlets of the vaporheaters.

It is to be understood that the upwardly inclined throat 170, directingrecirculated furnace gases toward the rear furnace wall 506, has itswall 502 formed by vapor generating tubes leading upwardly from a lowerheader 508 to the wall 506 and thence upwardly along that wall, aroundthe arch 510 and then, as screen tubes 512, in front of the secondarysuperheater section 40. Some of these tubes continue as roof sections514 over the roof of the furnace, and then to connections with the drum30. Others extend through the roof at 516 and connect at superposedpositions to the drum 30, as indicated at 518.

At the opposite side of the throat 170 the wall 500 is supported ordefined by vapor generating tubes leading upwardly from the front wallheader 520 along the upper throat wall 500 and then along the inclinedhopper bottom wall 522. These tubes then continue upwardly along theleft hand furnace wall 524, past the burners and then to connectionswith the drum 30. The side walls of the furnace are formed by closelyarranged vapor generating tubes having their upper ends connected tosuch headers as the side wall header 526 and their lower ends connectedto corresponding headers at the bottom of the furnace. These upper andlower headers are appropriately connected into the fluid circulation ofthe unit by appropriate circulators between the drum 30 and the upperheaders, and by appropriate downcomers leading downwardly from theliquid space of the drum 30. The lower ends of such downcomers areconnected to the side wall headers at the lower part of the furnace. Thestructure described immediately above also applies to the furnace 12which is shown in Fig. 1A and it is considered that the pertinentdescription need not be substantially duplicated with reference to thefurnace 12.

What is claimed is:

1. In a high capacity vapor generating and superheating unit, avertically elongated furnace having its walls defined by vaporgenerating tubes, an upright division wall including closely arrangedupright vapor generating tubes separating the furnace into two sections,exterior wall means forming a first gas pass leadinglaterally from onefurnace section, exterior wall means forming a second gas pass parallelto the first gas pass and leading from the other furnace section, saidgas passes and their adjacent walls being substantially spaced with afree access and maintenance space between the adjacent walls, fuelburning means for separately and independently firing the fur-.

naccs, stage 1 of a pendent vapor superheater including a bank ofupright tubes disposed in one of the gas passes, stage 2 of the samevapor superheater including another bank of pendent upright tubesdisposed in the other of the gas passes, and vapor conducting tubesconnecting the vapor outlet of stage 1 to the vapor inlet of stage 2,and means for conducting the superheated vapor from the outlet of stage2 to a point of use.

2. In a high capacity vapor generating and superheating unit, a furnacedefined by vapor generating tubes, a division wall including uprightvapor generating tubes separating the furnace into two sections, thedivision wall being constructed to provide furnace gas pressureequalization openings therein, a first gas pass leading laterally fromone furnace section, a second gas pass leading later,-

ally from the other furnace section, independent fuel burning means forseparately and independently firing the furnaces and thereby changingthe rates of gas flow through the furnace sections and the gas passes,other means for changing gas flows through the gas passes when changesin vapor generating rate occur, a reheater in one of the gas passes, afirst stage of a vapor superheater disposed in one of thegas passes, asecond stage of the same vapor superheater disposed in the other of thegas passes, and vapor conducting tubes connecting the outlet of thefirst stage to the inlet of the second stage and means for conductingthe superheated vapor from the outlet of the second stage to a point ofuse.

3. In a high pressure and high capacity vapor generating andsuperheating unit, a vertically elongated furnace with its boundariesdefined by closely arranged upright vapor generating tubes, other vaporgenerating tubes defining a division wall separating the furnace intotwo sections, a vapor and liquid drum disposed at the top of the unitand having the outlets of the vapor generating tubes communicatingtherewith, a gas pass leading laterally from the upper part of the firstsection of the unit and including a downpass, a reheater disposed insaid downpass, walls of said downpass having upright superheater supplytubes therealong, means conducting saturated steam from said drum tosaid superheater supply wall tubes, header .components disposed alongthe downpass walls at the bottom of said gas pass and having the outletends of the superheater supply tubes connected there to, a second gaspass leading laterally from the other section of the furnace andincluding a downfiow gas pass section having therein a plurality ofbanks of tubes of a convection primary superheater first stage, headercomponents disposed along the walls at the lower end of the downfiowsection of the second gas pass, conduits and superheater supply gas passwall tubes conducting steam from the drum to the header components ofthe second gas pass, conduit means conducting the steam from the headercomponents at the bottom of the first gas pass to the header componentsat the lower end of the second gas pass, and means conducting steam fromthe header components at the lower end of the downfiow section of thesecond gas pass to the convection primary superheater therein.

4. In a high pressure and high capacity vapor generating andsuperheating unit, a verticallylelongated furnace with its boundariesdefined by closely arranged upright vapor generating tubes, otherclosely arranged upright vapor generating tubes defining a division wallseparating the furnace into two sections, a vapor and liquid drumdisposed at the top of the unit and having the outlets of the vaporgenerating tubes communicating therewith, a first gas pass leadinglaterally from the upper part of the first section of the unit andincluding a downpass, a convection reheater including a bank of tubesdisposed in said downpass, walls of said downpass having superheatersupply tubes leading downwardly therealong, means conducting saturatedvapor from the drum to the upper ends of said superheater supply walltubes, header components disposed along the downpass walls at the bottomof said gas pass and having said superheater supply tubes dischargingthereinto, a second gas pass parallel to the first) of the second gaspass, conduits and superheater supply I gas pass wall tubes conductingvapor from the drum to the header components of the second gas pass,conduit means conducting vapor from the header components at the bottomof the first gas pass to the header components at the lower end of thesecond gas pass and means con ducting vapor from the header componentsat the lower end of the downflow section of the second gas pass to theconvection primary superheater.

5. In a high pressure and high capacity vapor generating andsuperheating unit, a vertically elongated furnace with its boundariesdefined by rows of upright vapor generating tubes, other vaporgenerating tubes defining division wall means separating the furnaceinto sections means independently firing the furnace sections, a vaporand liquid drum disposed at the upper part of the unit and having theoutlets of the vapor generating tubes communicating therewith, a gaspass leading from the first section of the unit and including adownpass, vapor heating means constituting the second stage of a primarysuperheater disposed in said downpass, walls of said downpass havingvapor supply tubes leading downwardly therealong, means conductingsaturated vapor from the drum to the inlets of said vapor supply walltubes, header means at the bottom of said gas pass having the outlets ofthe vapor supply wall tubes communicating therewith, a second gas passleading from the other section of the furnace and ineluding a downflowgas pass section having vapor heating tubes of a first stage of aprimary vapor superheater therein, header means disposed at the lowerend of the second gas pass, conduits and vapor supply wall tubesconducting vapor from the drum to the header means of the second gaspass, conduit means conducting the vapor from the header means at thebottom of the first gas pass to the header means at the lower end of thesecond gas pass, and means conducting superheater vapor from the firststage of the primary superheater to the vapor inlet of the second stageof the primary superheater.

6. In a high pressure and high capacity vapor generating andsuperheating unit, a vertically elongated furnace with its boundariesdefined by rows of upright vapor generating tubes, other vaporgenerating tubes defining a division wall separating the furnace intosections, a vapor and liquid drum disposed at the upper part of the unitand having the outlets of the vapor generating tubes cornmunicatingtherewith, a gas pass leading from the first section of the unit andincluding a downpass, vapor heating means disposed in said downpass,walls of said downpass having vapor supply tubes leading downwardlytherealong, means conducting saturated vapor from the drum to said vaporsupply wall tubes, header components at the bottom of said gas passhaving the outlets of the vapor supply wall tubes in communicationtherewith, a second gas pass leading from the other section of thefurnace and including a downflow gas pass section having therein aplurality of banks of vapor heating tubes constituting the first stageof a primary superheater, header components disposed along the walls atthe lower end of the second gas pass, conduits and superheater supplywall tubes conducting, saturated vapor from the drum to the headercomponents of the second gas pass, conduit means conducting vapor fromthe header components at the bottom of the first gas pass to the headercomponents at the lower end of the second gas pass, means conductingvapor from the header components at the second gas pass to the vaporinlet of the first stage of the primary superheater.

7. In a high capacity and high pressure vapor generating andsuperheating unit, two separately fired furnace sections each having itsboundaries defined by upright vapor generating tubes, the furnaces beingseparated by a division wall of vapor generating tubes with some of thedivision wall tubes arranged to present gas communicating passagesfreely communicating with the gas spaces of the furnaces, a first gaspass leading from one furnace, one stage of a secondary superheaterdisposed in said gas pass, a reheater disposed in said gas pass beyondthe secondary superheater stage, a second gas pass leading from theother furnace, a second stage of a secondary superheater disposed withinthe second gas pass, a primary convection. superheater disposed withinthe second. gas pass at a position beyond the second secondary super--heater stage, gas flow regulators for proportioning the flow of gasesbetween the respective gas passes for the purpose of regulatingtemperature of heated vapor, vapor flow connections establishing vaporflow from the primary superheater to the first stage of the secondarysuperheater and then to the second stage of the secondary superheater, arecirculated gas flow system for each of the furnaces and its associatedgas pass, and means for separately controlling each recirculated gasflow system for maintaining predetermined heated vapor reheattemperatures over a wide load range.

8. In a high capacity and high pressure vapor generating andsuperheating unit, two separately fired furnace sections each having itsboundaries defined by upright vapor generating tubes, the furnaces beingseparated by a division wall of vapor generating tubes with some of thedivision wall tubes arranged to present gas communicating passagesfreely communicating with the gas spaces of the furnaces, a first gaspass leading from one furnace,

a first stage of a secondary superheater disposed in saidgas pass, areheater wholly disposed in one of said gas passes beyond the firststage of the secondary superheater stage, a second gas pass leading fromthe other furnace, a second stage of a secondary superheater disposedwithin the second gas pass, a primary convection superheater disposedwithin the second gas pass at a position beyond the second secondarysuperheater stage relative to gas flow, means conducting generated vaporto the inlet of the primary superheater, means connecting the vaporoutlet of the primary superheater to the inlet of the first stage of thesecondary superheater, means conducting superheated vapor from theoutlet of the first stage of the secondary superheater to the inlet ofthe second stage of the secondary superheater, gas flow regulators forproportioning the flow of gases between the respective gas passes forthe purpose of regulating temperature of heated vapor, a recirculatedgas flow system for each of the furnaces and its associated gas pass forwithdrawing heating gases from a position beyond vapor heating means andintroducing the withdrawn gases into the furnace sections, and means forseparately controlling each recirculated gas flow system for maintainingpredetermined heated vapor temperatures over a wide load range.

9. In a high capacity and high pressure vapor generating andsuperheating unit, two separately fired furnace sections each having itsboundaries defined by upright vapor generating tubes, the furnaces beingseparated by a division wall of vapor generating tubes with some of thedivision wall tubes arranged to present gas communicating passagesfreely communicating with the gas spaces of the furnaces, a first gaspass leading from one furnace, one stage of a secondary superheaterdisposed in said gas pass, a vapor reheater wholly disposed in said gaspass beyond the secondary superheater stage, a second gas pass leadingfrom the other furnace, a second stage of a secondary superheaterdisposed within the second gas pass, a primary convection superheaterdisposed within the second gas pass at a position beyond the secondsecondary superheater stage relative to gas flow, means conductinggenerated vapor to the inlet of the primary superheater, meansconnecting the vapor outlet of the primary superheater to the inlet ofthe first stage of the secondary superheater, means conductingsuperheated vapor from the outlet of the first stage of the secondarysuperheater to the inlet of the second stage of the secondarysuperheater, gas flow control means proportioning the flow of gasesbetween the respective gas passes for the purpose of regulatingtemperature of heated vapor, a recirculated gas flow system for each ofthe furnaces and its associated gas pass for withdrawing partiallycooled furnace gases from the gas pass at a position beyond the vaporsuperheater or reheater and introducing the withdrawn gases into theassociated furnace, and means for controlling each reheated vapor over awide load range.

gamma 10. In a high pressure and high capacity vapor generating andsuperheating unit; a vertically elongated furnace with its boundariesincluding upright vapor gen erating wall tubes; other vapor generatingtubes presenting an upright division wall separating the furnace intofirst and second furnace sections; means for independently firing thefurnace sections; a single elevated vapor and liquid drum having theupper ends of the vapor generating tubes connected thereto; meansforming separate first and second gas passes leading from the first andsecond furnace sections respectively; a convection vapor reheater whollydisposed in the first gas pass; a convection section constituting astage of a primary vapor superheater disposed in the first gas pass downstream of the reheater in a gas flow sense; other convection tubesconstituting another stage of the primary superheater in the second gaspass; superheater supply wall tubes in each gas pass conducting vaporpassing from the drum to positions adjacent the inlets of the primarysuperheater stages; means conducting initially superheated vapor fromthe outlets of the superheater supply wall tubes of the first gas passto the vapor inlets of the primary superheater stage in the first gaspass, means conducting vapor from the outlets of the superheater supplywall tubes of the second gas pass to a position wherein the vapor fromthe second gas pass superheater supply wall tubes joins the vaporflowing to the first stage of the primary superheater; means conductingthe combined vapor flows from the outlet of the first primarysuperheater stage to the inlet of the second primary superheater stage;a secondary superheater in the second gas pass; means connecting thevapor outlet of the primary superheater second stage to the inlet of thesecondary superheater; and means for varying and controlling the heatinggas flows through the gas passes.

11. In a high pressure and high capacity steam generating andsuperheating unit, means including steam generating wall tubes defininga plurality of furnaces, means for independently firing the furnaces,means connecting the steam generating wall tubes of the separatefurnaces to a common steam collecting means, means forming separated gaspasses conducting gases from the separate furnaces, steam superheatingmeans receiving the steam generated in the wall tubes and heated by thegases in a plurality of the gas passes, a convection steam reheaterdisposed wholly within one gas pass, and means other than the fuelburning means for varying the flow of gases through the gas passes, thesteam superheating means including a convection primary superheater withseries connected parts one of which is disposed downstream of thereheater and in its gas pass and the other of which is disposed inanother gas pass, said superheater means also including a secondaryconvection superheater section in the gas pass containing said reheaterand arranged to receive steam from said primary superheater, and asecond secondary convection superheater section in said other gas passarranged to receive superheated steam from said first secondarysuperheater section.

12. In a high capacity vapor generating and superheating unit, uprightvapor generating tubes defining the boundary surfaces of a large volumevertically elongated furnace chamber having generally rectangularhorizontal cross section with its major dimension much greater than itsminor dimension, a pair of spaced and separately walled gas passesextending laterally from the upper part of a longer side of the furnace,convection fluid heat exchange devices arranged in each said gas passes,the

separate gas pass constructions leading from and spaced apart along thelonger side of the furnace to permit maintenance access to the adjacentinner sides of the two parallel gas passes, spaced and separate downflowgas pass constructions leading downwardly from said parallel gas passes,said convection fluid heat exchange devices including a first stage of aprimary superheater in the downflow part of one of the gas passes, asecond stage of the primary vapor superheater disposed within thedownfiow gas pass for the other lateral gas pass and connected in seriesas to steam flow with said first stage primary superheater, a firststage of a secondary convection superheater disposed within the otherlateral gas pass, tubular connections conducting vapor from the vaporoutlet of the second stage of the primary superheater to the first stageof the secondary superheater, a second stage of the secondarysuperheater disposed in the lateral gas pass leading to the downflowpass having therein the first stage of the primary superheater, tubularconnections conducting vapor from the outlet of the first stage of thesecondary superheater to the inlet of the second stage of the secondarysuperheater, and a reheater disposed in one of said lateral gas passes.

13. In a steam generating and superheating unit, vapor generating tubesdisposed in wall formation and arranged to define a hopper bottomfurnace of rectangular horizontal cross-section, fuel burner means at alevel above that of the hopper bottom effecting the burning of fuel insuspension within the furnace at vary ing rates and directing burningfuel from one vertical furnace wall toward an opposite furnace wall,wall means providing a superheater gas pass opening to the upper part ofand receiving combustion gases from the furnace, a convectionsuperheater including a bank of spaced tubes arranged across the gaspass, means conducting steam from the Wall tubes to the superheater, anda gas recirculating system including ductwork having an inlet receivinga proportion of the combustion gases at a position downstream of thesuperheater and causing such gases to flow into the furnace through thehopper bottom, said hopper bottom having a pair of substantiallyparallel inclined walls arranged to form an elongated ash dischargethroat opening at its upper end to the lower end of said hopper bottomand inclined in a direction intersecting the furnace wall opposite saidfuel burner wall at an elevation below the elevation of the fuel burnermeans, and said gas recirculating system ductwork opening into the lowerportion of said ash discharge throat at a point spaced from the upperend thereof a distance suflicient to provide a stream of recirculatedcombustion gases flowing into said hopper bottom towards said oppositefurnace Wall.

References Cited in the file of this patent UNITED STATES PATENTS1,922,663 Kemnal Aug. 15, 1933 1,931,948 Armacost Oct. 24, 19332,334,187 Frisch Nov. 16, 1943 2,677,354 Epley May 4, 1954 2,781,746Armacost et al. Feb. 19, 1957 FOREIGN PATENTS 503,778 Belgium June 30,1951 499,583 Belgium Dec. 15, 1950 682,121 Great Britain Nov. 5, 1952609,674 Great Britain Oct. 8, 1948 523,871 Great Britain July 24, 1940

